“The causes of this event have not been determined yet, so it’s too early to talk about [possible causes],” he said. “The investigation will show. Certainly, we will consider all variants, common, criminal, first of all, of a terrorist nature.”

It’s likely Russian officials are considering a deeper cause given that Putin was nearby giving a speech at a media forum in St. Petersburg.

“The explosion happened between the Sennaya Ploshchad station and Tekhnologichesky Institut at around 2:40pm local time, Russia’s National Anti-Terrorism Committee said,” reported RT. “The blast was caused by an unidentified explosive device, officials announced, adding that all metro stations in St. Petersburg have been closed.”

“The metro is basically fully evacuated, according to Russia’s National Anti-Terrorism Committee.”